whizz wheel

[BigEndBob]

Isn't it about time only one method was taught when using the reverse of the whizz wheel when finding groundspeed and drift and all the different methods shown in study books scrapped.

If the vector triangle solution is transfered from basic principles to the computer there is only one correct, straightforward method to arrive at an answer.
All this fiddling about to make things fit using alternative methods only leads to confusion or lack of understanding of whats going on.
I've lost count the number of Skill Test candidates on presenting their flight plan to find drifts applied in reverse, of incorrect value and Tas becomes groundspeed. (Notwithstanding these should be double checked by applying some logic).

Instructors are at fault, most don't understand the mechanics of vector triangle and pass on whatever they were shown/taught to their students.
In Nav. exams you can always tell who as used the alternate methods the answers are always 1 degree or 1 knot out.

These alternate methods only exist to ensure that the wind vector arrow/line always ends up below the centre dot.

If whats going on was fully understood it doesn't matter where the line goes so long as its logical and correct.

.....i will now retreat to my bunker.......SH:ugh:

[StrateandLevel]

Not sure which you regard as the "alternative" method. The Dalton Computer was designed to be used Wind DOWN. Most people who use Wind UP claim there is less fiddling rather than more however, it can lead to the wrong conclusion.

Personally I'd prefer the student to use Max drift and head/ tail components leaving the wheel in its box.

[GT]

BigEndBob,

For what it's worth, I agree with you entirely. However, I think you'll find that we are in the minority (which doesn't make us wrong!).

StrateandLevel,

I find myself in agreement with you as well. When I teach navigation I initially do so using max. drift etc., then progress onto the whizz wheel.

Regards, GT.

[Mark 1]

BigEndBob,

I agree with you entirely. Wind dot up is the only logical way to do it.

I've shown students this method, drawn the vectors on for them and explained what I was doing, and they understood straight away.

I also managed to do all the exercises in the CPL exams this way with no problems whatsoever. I've yet to see a logically reasoned argument for wind dot down.

But they'll probably never use it again once they've qualified anyway.

[juswonnafly]

I agree with S&L on this. I teach my studes max drift method. The only ones who get lossed/confused are those who insist on using the whizzwheel!

JWF :D

[john_tullamarine]

While I agree that the "conventional" techniques are the way to go, it is important to realise that wind up and wind down will give the same answer (provided that the "unconventional" user keeps his or her cool) ... ie there is no inherent error in using one technique as opposed to the alternative. Same applies for either Dalton or Jepp styles of whizz wheel. This thread (http://www.pprune.org/forums/showthread.php?s=&threadid=66361) gives a bit of explanation.

[pilotbear]

I also use Max Drift for navigation with my people, it also helps them when diverting etc. as it can be done visually on the map with a wind vector arrow.
I also visually estimate groundspeed for timings, i.e.
If you have any tailwind within 60 deg of track divide distance by two for the time. (120kts g/s)
If no h/w or t/w within 60 deg of track then take 2/3 of distance for your time. (90kts g/s)
If you have any headwind within 60 deg of track then distance = time. (60kts g/s)
This is at TAS cruise of 90 - 100 kts. You may say this is inaccurate, but how many PPLs can fly that accurately and how often is the wind correct?

It can be a little more complex/accurate if required but still easy to do visually or mentally.

The whizz wheel is good for more complex stuff if the person is interested but that is all in my humble opinion. Not necessary for Mr PPL.:ok:

ps If I have to use the infernal device I draw direction arrows on the wind line >>> or <<< and direction lines on the track line >> or << then seeing the drift effect is easy whichever method you use.:)

[BigEndBob]

The thread that John refers to proves my point, these alternate methods have been created to make someones life easy.
i.e. people teaching solutions to problems that few use other than to pass commercial exams, then forget. So poor ppl students have to suffer some cock handed method to find the solution to the most common problem, finding drift and groundspeed.

Bravo..i applaued those that use methods,whatever they may be, to guesstimate what the final values should be. This holds the student in good stead for practise /real diversions (and later IMC holds. etc.).
I am amazed how few students/candidates for test actually mark the wind arrow on their chart. After track this should be the next line drawn on the chart. How many times have i told a student to mark on the chart the wind vector before i go about explaining how to correct their errors.

[BigEndBob]

Also from my ATPL study days i seem to remember the basic CRP-1 being more accurate than the CRP-5 because of the smaller speed a drift line spread. Could never understand why everybody dashed out to upgrade their computer for ATPL exams, because it had the compressibilty solving bit on it i suppose and its BIGGER.

[Flying Boat]

BEB

You need the CRP5 to answer the 3 or 4 compressability questions in ATPL Gen Nav.

Then the CRP1 is fine.

FB

[BigEndBob]

When i did my ATPL you were allowed to use the compressibilty table provided by CAA , is this still true?

[Flying Boat]

Didn't see any Comp table, but did my Gen Nav in April, they still have a Sin & Cosine table, may be on the back.

We were taught how to do comp on the CRP5 as part of the course. I am doing JAR so it might be different now.

[destructor]

Draw the track and wind lines on the map know the max drift and lets go. I have yet to meet the MET man who can get the wind speed and direction right so why spend time with a whiss wheel for accuracy when the start figures are wrong anyway. To navigate learn the map/route use max drift calc and adjust!

[Pianorak]

I started off doing wind-mark UP (method A in Trevor Thom), but was persuaded to drop that and do wind-mark DOWN. Got rather confused and reverted to UP.
But who is this Max Drift? Haven't come across him yet. Can you use Max D. to calculate HDG and GS? Will some kind soul please explain - have the nav exam coming up in couple of months’ time.
:{ ;)

[Obs cop]

The key with a dalton computer is basically to ignore it until there is a thorough understanding of the vector triangle.

I certainly found that once this was lodged in my thick skull, I could easily used either wind up or wind down at my discretion. Moreover, the whizz wheel/ max drift mental DR techniques are not there to be used individually. Each have their advantages and disavantages depending on the flight planned and subsequant execution of that flight.

IMHO

Obs cop

[Send Clowns]

The techniques for mental ded reconning are excellent, and all students should know them. I used to pre-flight plan without a flight computer pertfectly adequately.

BigEndBob

The CRP-1 is smaller and so less precise than the CRP-5. The CAA admit some of the JAA ATPL answers are unreasonably close together even for the latter, it would be impossible to distinguish the answers on a CRP-1. For practical navigation the CRP-1 is perfectly adequate, but do not confuse apparent greater accuracy with precision.

No compressibility tables are offered in the exam, and they are no longer taught on the course. The flight computer is the only realistic option.

The given answers are calculated using a Pooley's CRP-5, so the student would be wise to do likewise even without these other factors. Having used 4 different flight computers, now teaching ATPL General Navigation and Flight Planning I would say that the this is the best of these instruments I have come across.

ObsCop

I agree - I teach ATPL students the vector triangle first, as I learnt to navigate a ship/boat. I then transfer this to a CRP-5 (wind down)

[pilotbear]

Pianorak,

Max drift method of calcualting hdg and g/s is not accurate for the written exams but is good for actual nav and diversion planning.
With the wind up/down argument, if you make the wind line an arrow showing the direction of the wind and remember that the TAS goes on the back of the arrow the concept is relatively easy either way. Read the hdg and g/s off the pointy end of your arrow.

Max drift:
An aeroplane at a constant tas with a constant 90deg crosswind will always experience a maximum amount of drift.

calculation; windspeed/TAS X 60

i.e. 20kts/100kts X 60 = 12deg. write this on your map with a big wind arrow. The hdg is worked out as follows VISUALLY.

So, at 100kts tas this aircraft will drift 12deg with a 90deg xwind, so you steer 12deg into the wind.

How do you work it out if the wind is not 90deg off the track?

Use the watch face concept, (that is 15mins=1/4hr, 30mins=1/2hr etc)

so if the wind is 15deg off the track use 1/4 max drift,
if 30deg use 1/2 max drift,
if 45deg off use 3/4 max drift,
if 60 or more off the nose use all the max drift to work out your heading.
(in the right direction of course).

Use the same concept in reverse for g/s;
(add or subtract from TAS, check visually on your map.
If the wind is up to 30deg off the track use all the wind speed
If 45deg off the track use 3/4 of the windspeed,
If 60deg or more use 1/2 the wind speed etc.

this can be as accurate as you want to make it and there is a cheap book that explains this well. 'Diversion planning' by Martyn Smith:ok:

[Pianorak]

Thanks pilotbear Having just had a drink (couple of glasses of red wine) it makes perfect sense. . . However, may have to have recourse to Diversion Planning to hammer the message home completely. :hmm:

[BigEndBob]

Sendclowns....i seem to remember the fans lines being wider apart on the smaller CRP-1 because of the greater effect of drift on lower speeds.
CRP-5 are closer together (therefore less accurate) because of the higher speeds that can be plotted on it. (But the exam questions never seem to require speeds behond those on the CRP-1).

[Send Clowns]

The CRP-1 and CRP-5 cover similar speed ranges. At lower speeds the CRP-5 has fewer drift lines than high speed, though this is a penalty not the benefit you suggest.

The width of spacing of the drift lines does not affect accuracy, and although it can affect precision closer drift lines can only increase precision, not reduce it. The width apart of the fan lines is basically determined by the drift experienced and the scale being used, i.e. is each drift line one or two degrees. Given that the correct answer to the same problem does not change, closer fan lines can only mean finer detail, i.e. going down from 2 degrees per line to 1 (from 100 kts slow side, 300 kts fast side on a CRP-5). These closer lines can only make the instrument more precise, not less!

In fact I believe the CRP-5 vector calculator side is pretty much a CRP-1 scaled up. Therefore the larger size must improve precision, as the eye can read it more easily and the pencil mark is thinner in comparison.

I cannot see any way in which a CRP-5 can possibly be less accurate than a CRP-1.

[hugh flung_dung]

For IMC students I teach a modified version of the MaxDrift technique described by Pilotbear.
Calculate MaxDrift before flight, draw the arrow on your chart.
Turn so track=heading.
Look at the DI, mentally drop a vertical line from wherever the wind direction is shown until it bumps into the horizontal line through the centre of the DI. The radius of the DI equals MaxDrift so the proportion of the radius between the centre and where the vertical line touches it is the proportion of MaxDrift on that track. Turn towards the wind by the proportion of MaxDrift.

By projecting a horizontal line from the wind to the vertical axis and saying that the radius of the DI equals the wind speed you can calculate the head/tail wind. Calculate all legs using still air and then modify the times by whatever percentage the head/tail wind is of the TAS.

Highly accurate, no complicated mental gymnastics. No gadgets.

This reads horribly but it's simple if you draw a diagram:D

[pilotbear]

Very nice, I am going to try that. A nice way of describing the proportion without using maths.:ok: